User interfaces are the links between humans and devices used to accomplish tasks. User interfaces may be as simple as a sign or label stating “push” to indicate where to push, for example, to open a door, or may involve hardware integrated with software, changing, for example, visual displays, voice recognition, etc. Activation or selection or the function to be performed may be done in a variety of ways; including physical contact such as touching a button, switch, as well as motion or thermal detection.
Selection of a function and actuation of that function without physical contact can have benefits including: reducing or eliminating damage to the interface from contact, contamination or the interface and user, repetitive stress injury to the user, etc.
User interfaces typically do not have just functional requirements. The interfaces often have aesthetic requirements so that they are visually interesting, visually pleasing or even not visible until the time of use, or visible only by the user. User interface appearance can influence a user's perception of the quality and craftsmanship of the device (e.g., how well the interface blends in with the device).